The invention relates to a cast steering knuckle for a vehicle and a vehicle comprising a cast steering knuckle.
It is known to use cast steering knuckles for suspension of wheels for commercial vehicles, particularly trucks. For making more efficient commercial vehicles available, one is desirous to equip such vehicles with hydraulic driven steered wheels. Necessary fluid connections are fed through the steering knuckles. This is achieved by drilling channels in the cast body of the steering knuckle for supplying hydraulic oil to the hydraulic wheel motors. However, available lengths and widths of the drilled channels are restricted as well as the density of channels.
It is desirable to provide an improved cast steering knuckle comprising fluid channels enabling an optimized flow of fluid, wherein the optimized flow has reduced losses. It is also desirable to provide a vehicle comprising an improved cast steering knuckle.
A cast steering knuckle is proposed for a vehicle, particularly a commercial vehicle, more particularly a truck, comprising a knuckle body. One or more pipes, each comprising a pipe body, are moulded into the knuckle body providing one or more channels in the knuckle body as ducts for a fluid and/or one or more electrical harnesses.
Preferably, the channels can be provided for transporting a fluid. Fluids in terms of the invention can be liquid, e.g. hydraulic fluid, or gaseous, e.g. compressed air. The flow resistance in the pipe(s) has a large influence on the flow of fluids. Losses caused by the flow resistance can influence the flow velocity, the pressure and/or the temperature of the fluid in a way, that the function of a device placed at or near the steering knuckle, e.g. a hydraulic wheel motor or a central tire inflation system (CTIS), is disturbed. The flow resistance can substantially be influenced by bends of the pipe(s) and the roughness of the inner surface of the pipe(s). One or more channels can also be used as a feedthrough for one or more electric cables.
Favourably, the design of the steering knuckle according to the invention makes it possible to reduce the flow resistance and to improve the flow of the fluid compared to techniques such a drilling channels or forming channels by casting the knuckle with sand cores in desired positions of the channel. The routing and the surface of the fluid channel are defined by the one or more moulded-in pipe. In this way an improved flow resistance even for very complex routing and/or long fluid channels comprising several bends can be achieved.
Favourably, before the moulding-in, the one or more pipes can be performed to and bent in various directions and angles according to a desired design. Particularly in bends, the inner surfaces of the one or more pipes are smooth and nicely bent thus yielding a favourable low flow resistance. With the technique of drilling channels smoothly bent channels or channels with complex routing cannot be achieved.
Favourably, it is easy to manufacture pipes with smooth inner surfaces. By casting the knuckle body employing sand cores according to the known art for the fluid channels, the inner surfaces of the channels are rough compared to the inner surfaces of the inventive pipe because of the structure of the sand grains. Further there is a risk that sand grains may remain in the channel and contaminate the fluid.
Favourably, the routing of the one or more pipes in the cast steering knuckle can be optimized against weight and stability of the cast steering knuckle and the steering properties.
According to a favourable embodiment of the invention, the one or more pipes can be equipped with at least one fitting before casting the knuckle body. Such fittings can be mounted easily before casting the knuckle body, particularly if the fittings have to be placed in areas of the knuckle body which are difficult of access. The fittings provide easy connections to other pipes or equipment outside the steering knuckle. Favourably, the one or more pipes can be preassembled thus facilitating the manufacture of the steering knuckle.
According to a further favourable embodiment of the invention, one or more pipes can be equipped with at least one front mounting which integrates one or more free ends of the one or more pipes. The free ends can be protected during the casting process. The front mounting can also create or maintain a well defined shape of the free ends thus facilitating to connect the free ends to a fitting or a pipe connector. Further, the front mounting can be adapted for holding the one or more pipes in the knuckle body in position during the moulding process. Besides this the front mounting can be adapted for sealing the free ends of the pipes during the casting process particularly to prevent molten material to enter the one or more pipes. Advantageously, the front mounting can provide areas which allow a torsionally stiff connection to an axle, e.g. for reliably handling high torques when a hydraulic motor attached to the steering knuckle.
According to a further favourable embodiment of the invention, at least one of the one or more pipes can be bent at least by 90°. In this way an optimization of the pipe routing can be achieved. Bending the one or more pipes by more than 90° can also be achieved thus allowing using available space in the knuckle body. Such a shape of the channel can hardly be achieved with drilling or sand core casting.
According to a further favourable embodiment of the invention, the bending radius of one or more pipes can be larger than the inner diameter of the respective pipe. This can favourable reduce the pressure drop of a medium flowing in the pipe. For instance, the bending radius can be at least twice as large as the inner diameter.
According to a further favourable embodiment of the invention, at least one of the one or more pipes can be bent at least in two dimensions. Thus very complex pipe routings can be realized, which is virtually impossible with known art techniques such as drilling channels.
According to a further favourable embodiment of the invention, the pipe body of at least one of the one or more pipes can have one or more hydroformed portions along its pipe body. Of course, the complete pipe body can by manufactured by hydroforming. Hydroforming is a cost-effective way of shaping malleable metals into lightweight, structurally stiff and strong pieces. Hydroformed pipes or portions of pipes can be very nicely bent and can have very smooth inner surfaces which are favourable for a low flow resistance of the pipes. Different from using sand cores or drilling the channel, there is no risk that particles, i.e. sand grains, rubbings or wear debris, remain in the channel. Further, by hydroforming portions of the pipe body, the cross section of the pipe body can be increased where enough space is available for the channel in the knuckle body and decreased at positions where space in the knuckle body is restricted. Thus, such hydroformed pipes make it possible to provide flow-optimized cross-sections of the pipes. Particularly, the cross-section can vary along the length of the pipe for providing a flow-optimized pipe. More particularly, the cross-section can have a profile which makes use of locally available space. The cross-section is not necessarily circular but can be of any form, such as elliptic or angled, e.g. triangular, square-shaped or of a more complex shape where appropriate. The cross-section can change from a round, e.g. circular or elliptic to an angled cross-section and vice versa along the length of a pipe, which allows for a very flexible design of the pipes and an improved usage of available space inside the steering knuckle.
Preferably at least one of the one or more pipes can have a hydroformed body. Thus the whole pipe body can easily be formed in only one step.
According to a further favourable embodiment of the invention, at least one of the one or more pipes can have a length of at least five times, preferably at least eight times the diameter, particularly the outer diameter. Thus long fluid channels can be achieved in the cast steering knuckle, since pipes with pipe bodies are stable even if they are long compared with their diameter. “Long” means that the length of the channel is at least five times of the diameter, preferably at least eight times the diameter. With other techniques known in the art like using a sand core, the length of the channel is limited, since a long sand core with a small diameter will break.
The cross sections of the pipes are not necessarily circular but can have an oval shape, a triangular shape, a square shape or any cross section which is desired. It is even possible for optimizing the usage of space in the knuckle body and/or for adapting the flow resistance or the flow properties of the pipes to provide one or more pipes with varying diameters and/or cross sections along their extensions.
According to a further favourable embodiment of the invention, the one or more pipes can be concentrated in a middle portion of the knuckle body. In this way the stability of the cast steering knuckle can be improved. Further the pipes can be protected by the surrounding material of the cast steering knuckle. Another advantage is that heat compensation between the fluid in the pipe and the knuckle body can be improved.
According to a further favourable embodiment of the invention, the one or more pipes can be fixed together before casting the knuckle body. In this way the one or more pipes can be held in position during casting of the knuckle body.
In accordance with a further advantageous embodiment of the invention, cast material of the knuckle body can be arranged between the one or more pipes. Thus the stability of the knuckle body and the pipes can be further improved. Besides this, the cast material can act as a thermal isolation between the pipes. On the other hand, the cast material can further improve the heat compensation between the fluid in the pipes and the knuckle body.
According to a further favourable embodiment of the invention, at least one of the one or more pipe bodies can be provided with a surface coating at the outer surface. In this way the contact between the cast material and the pipe can be optimized. Particularly, the flow ability of the cast material along the pipe during the casting process can be improved, so that in particular blistering in the cast material near the outer surface of the pipe can be prevented. It is also possible to provide a coating at the inner surface of the one or more pipes for e.g. corrosion protection or the like. Favourably, the inner surface can be treated before casting the knuckle body.
Particularly, the surface coating at the outer surface can comprise zinc or tin. Zinc and tin are well-suited as surface coatings in particular for preventing blistering in the cast material.
In accordance with a further favourable embodiment of the invention, at least one of the one or more pipes can be provided as duct for a hydraulic fluid. Thus the cast steering knuckle can be used for hydraulic devices such as hydraulic wheel motors for hydraulic driven steered wheels.
According to a further favourable embodiment of the invention, at least three pipes can be contained in the knuckle body particularly for driving a hydraulic motor mounted on the steering knuckle. In this way the pipes can be adapted for transporting fluid with different specific functions and/or characteristics. In particular two pipes can be adapted for inflow and outflow of fluid for driving the hydraulic wheel motor and one pipe e.g. for draining.
According to a further favourable embodiment of the invention, at least three pipes can be casted in the axle part of the steering knuckle. The axle part of the steering knuckle is the part where the hydraulic fluid has to be transferred to the rotating hydraulic motor.
According to a further favourable embodiment of the invention, at least four pipes can be contained in the knuckle body. In this way the pipes can be adapted for transporting fluid with different specific functions and/or characteristics. In particular two pipes can be adapted for inflow and outflow of fluid for driving a device, e.g. a hydraulic wheel motor, and two pipes can be adapted for inflow and outflow of fluid for controlling the device. It is also possible to use the pipes for different liquid or gaseous fluid(s) in particular for controlling and/or driving the device. As the steering knuckle can be provided for bearing a motor, the pipes can be used for transporting hydraulic oil, coolant particularly for supplying a hydraulic motor, as well as be used as feedthrough for electric harnesses used for connection to sensors and/or actuators or a power supply of e.g. an electric motor instead of a hydraulic motor attached to the steering knuckle.
Preferably, pipe diameters can be between 10 to 20 mm. One or more pipes can have varying diameters from one end to the other end. For transporting fluids, particularly under high pressure, to and from a hydraulic motor attached to the steering knuckle it is advantageous to provide pipes with diameters as large as possible to be able to supply the necessary amount of hydraulic oil and/or coolant to the hydraulic motor. A hydraulic motor needs a very high flow of hydraulic oil during operation. In a steering knuckle, however, size restrictions apply. Particularly hydroformed pipes provide the possibility to vary the diameter of the pipes along their extension and to optimize the cross-section in such a way. Pipes with smaller diameters can be used for low pressure fluids, e.g. for a fluid with constant pressure, for draining and for electric cables, e.g. for sensors, actuators and the like.
The invention is not limited to cast steering knuckles with hydraulic wheel motors. The invention can be applied to installations with central tire inflation systems (CTIS). In this case the pipe(s) is/are adapted for transporting compressed air.
According to a further aspect of the invention, a vehicle, particularly a commercial vehicle, more particularly a truck, is proposed with the inventive cast steering knuckle. Wheels are coupled to the cast steering knuckles provided with a hydraulic motor. So it is possible to realize a vehicle with hydraulic driven steered wheels with all advantages of the invention.